1. Field of the Invention
The present invention is broadly concerned with web-fed offset lithographic printing towers of modular construction. More particularly, the invention is concerned with a modular printing tower which is especially designed for ease of manufacture, repair and maintenance, and which can be easily and quickly varied in the field by removal and replacement of the printer module associated therewith, so as to vary printing characteristics as desired. Interchangeability of tower modules allows a user to maintain, at relatively lost cost, spare and/or different modules for convenience purposes and to increase the versatility of the tower.
2. Description of the Prior Art
Traditionally, complete web-fed offset lithographic printing presses are composed of a series of aligned towers through which a continuous web of paper is fed for printing purposes. In the case of color printing for example, a separate tower is used for each color so as to give the final printed material a multicolor effect. Also, each press tower is normally provided with a printer section, one or more inking units, and associated water systems.
For the most part, web-fed press towers of the type described above have been produced on an individual basis. This has generally involved fabricating sidewalls and other necessary support structure, and installing the necessary rollers and other mechanism associated with the tower. In this connection, the practice has been to employ relatively thick, integral tower sidewalls. These sidewalls are carefully bored for receiving roll mounts at various locations, as well as being configured for other purposes. As can be appreciated, such a mode of construction presents a number of problems. First, use of integral sidewalls makes it necessary to discard the entire sidewall in the event that a small error is made in placement of a single aperture therethrough, inasmuch as roll placement and orientation are critical to tower performance. Hence, a single mistake of this nature in fabrication makes it necessary to scrap an entire sidewall, even if it is otherwise complete and perfect. Second, even though only a portion of the overall tower (normally the printer section) requires relatively thick sidewalls for adequate support, use of integral sidewalls means, as a practical matter, that the entire sidewall must be of the maximum thickness. This in turn greatly increases the material costs, without an attendant significant increase in structural integrity or utility of the tower.
Although towers having interchangeable printer sections have been proposed in the past, for the most part these units have been very complex and time consuming to use and modify. Certain known prior towers have employed printer sections which can be shifted horizontally for removal from the tower. Without known exception however, this type of tower has required specialized guide and motive structure for movement of the printer section, along with mechanism for shifting adjacent rollers and/or gears for accommodating a replacement printer section. All of the features have made variable presses extremely expensive and difficult to use in the field. In fact, these difficulties have been so formidable as to preclude production of certain types of variable towers, i.e., so-called variable straight through perfector towers having upper and lower web-contacting and printing blanket rolls for receiving a web traveling along a generally horizontal path of travel. The complexity of such straight through perfector towers has made it impossible to provide an effective capacity for varying the printing section of the tower, even though from a utility standpoint such a feature would be highly advantageous.